This invention relates to shaped explosive charges and, more particularly, to shaped explosive charges for stimulating oil well production, and the like. This invention was made with government support under Contract No. W-7405-ENG-36 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
Extracting all or most of the petroleum from an oil field has been a goal for many years. Petroleum generally is not found in underground pools, but is found within rock strata and flows along rock fractures to various collection points for production. In production wells, boreholes are drilled into a petroleum-bearing rock strata and the holes are typically lined with steel casings that are cemented in place. The casings are perforated in place to form radial fractures from the casing wall into the surrounding rock to permit petroleum to flow into the well bore.
Conventional perforating techniques include bullets fired through the casing into the surrounding rock, hydraulic perforating and fracturing, and explosive shaped charges. Explosive devices are used to perforate production casing within a borehole and to fracture the rock surrounding the borehole to increase the permeability of the oil-bearing rock strata near the borehole and increase the fluid flow into the production casing.
It will be appreciated, however, that space for explosive devices is limited by the size of the production casing. Also, the casing must be perforated without destroying the integrity of the casing and causing the surrounding borehole to collapse. These effects limit the effectiveness of conventional explosives. Shaped charges have been used to increase the volume of rock strata fractured by the explosive charge, but an increased volume that is fractured is high desirable.
Accordingly, it is an object of the present invention to provide for increased fracture volume in a rock strata surrounding the borehole casing about a production zone.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.